CN107063430A - MEMS based on piezoresistive effect is with the spherical oscillator vector hydrophone of the vibration shape - Google Patents

Abstract

The invention discloses a MEMS co-vibration spherical vibrator vector hydrophone based on the piezoresistive effect, which comprises a frame-shaped base, and four sides on the frame-shaped base are respectively connected to an annular connecting body through beams, and the annular connecting A spherical vibration pickup unit is installed on the body, and the density of the spherical vibration pickup unit is 1g/cm ³ ; varistor R ₁₁ , varistor R ₁₂ , varistor R ₁₃ and varistor R ₁₄ , the frame-shaped base is provided with a reference resistor R2, a reference resistor R3 and a reference resistor R4; the piezoresistors R ₁₁ , R ₁₂ , R ₁₃ , and R ₁₄ are connected in series with the reference resistors R2, R3 and R4 through metal The leads are connected in a Wheatstone bridge configuration. Based on theory, the present invention designs and optimizes a co-vibration spherical oscillator vector hydrophone with miniaturization, good low-frequency characteristics, high sensitivity, wide operating frequency band, common-mode output and differential-mode suppression.

Description

MEMS synchronous spherical vibrator vector hydrophone based on piezoresistive effect

technical field

The invention relates to a vector hydrophone in the field of MEMS sensors, in particular to a MEMS co-vibration spherical vibrator vector hydrophone based on the piezoresistive effect.

Background technique

At present, the vector hydrophones developed at home and abroad are generally divided into two categories: co-vibration type and differential pressure type. For the differential pressure vector hydrophone, because the depth of the "8" cosine directivity pit is too shallow, the pointing accuracy is not high, which limits its application in the field of underwater acoustics. For the co-vibration vector hydrophone, according to the different sound wave receiving theories of the particle velocity hydrophone, the co-vibration vector hydrophone can be divided into the co-vibration cylindrical oscillator vector hydrophone and the co-vibration spherical oscillator vector hydrophone device. Conventional co-vibration vector hydrophones must be fixed on a rigid frame with elastic suspension elements (such as rubber ropes or metal springs, etc.), and the mechanical characteristics of the suspension elements directly affect the electroacoustic performance of the hydrophone. This type of vector hydrophone is uniformly arranged with one or more acceleration sensors in the center or inside of the vibration pickup unit to measure the vibration velocity and acceleration of the vibration pickup unit, so as to obtain relevant information about the particle velocity in the sound field. Due to the problems of low sensitivity, large mass, mismatch between acoustic impedance and water, and difficulty in using on small-volume platforms due to conventional design and processing technology. The MEMS vector underwater acoustic sensor has a series of advantages such as small size, high sensitivity, good vector performance and consistency. At the same time, the piezoresistive sensor has better low-frequency or even zero-frequency characteristics; based on this, the present invention proposes a method based on MEMS co-vibration spherical vector hydrophone with piezoresistive effect to meet the requirements of very low frequency detection.

Contents of the invention

The present invention solves the problem of poor anti-flow noise performance, low sensitivity, poor anti-shock performance, high quality, mismatch between acoustic impedance and water, and low-frequency characteristics of the spherical vibrator vector underwater acoustic sensor brought about by existing technical solutions such as conventional design and processing technology. In order to solve the poor problem, a MEMS co-vibration spherical vibrator vector hydrophone based on the piezoresistive effect is provided.

The present invention is realized by adopting the following technical solutions:

A MEMS co-vibration spherical vibrator vector hydrophone based on the piezoresistive effect, comprising a frame-shaped base, the four sides of the frame-shaped base are respectively connected to an annular connecting body through beams, and a spherical connecting body is installed on the annular connecting body. A vibration pickup unit, the density of the spherical vibration pickup unit is 1g/cm ³ ; piezoresistors R ₁₁ , piezoresistors R ₁₂ , piezoresistors R ₁₃ and piezoresistors R ₁₄ are arranged on the outside of the four beams respectively. The frame-shaped base is provided with reference resistor R2, reference resistor R3 and reference resistor R4; varistors R ₁₁ , R ₁₂ , R ₁₃ , R ₁₄ are connected in series with reference resistors R2, R3 and R4 through metal leads to form a Wheat bridge structure.

The invention adopts the micro-nano processing technology to realize the miniaturization of the spherical vibrator vector hydrophone. And the signal acquisition piezoresistors are arranged on the four beams connected with the spherical vibrator, so that the acoustic signal component in the direction perpendicular to the beams can be detected. When the hydrophone is affected by the acoustic signal from the Z direction, the stress distribution and change on each beam are exactly the same, and the piezoresistors R ₁₁ , R ₁₂ , R ₁₃ , and R ₁₄ are connected in series, etc. Effective as a varistor R1. The strain resistance R1 is equal to the resistance of the reference resistors R2, R3, and R4, and the varistor and the reference resistor form a Wheatstone bridge; the reference resistors R2, R3, and R4 are respectively used as the unilateral reference bridge arm of the Wheatstone bridge. Resistor R1 acts as a unilateral strain bridge arm of a Wheatstone bridge.

The symmetrical distribution of the present invention in the XOY plane, when being subjected to the acoustic signal action from the horizontal direction, two crossbeams on the same direction are respectively subjected to tensile stress and compressive stress (Fig. 4) equal in size, and the pressure sensitive One of the resistors increases, the other decreases, and the resistance changes are equal; therefore, the resistance of the vector hydrophone equivalent piezoresistor R1 remains unchanged, and the bridge is in a balanced state. Therefore, this structure can effectively improve the output of the acoustic signal component from the Z direction, and suppress the output of the acoustic signal component from the X or Y direction.

According to the sound wave receiving theory of the particle velocity hydrophone, when ka << 1 (k is the wave number of the sound wave, a is the diameter of the vibration pickup unit), the sound field near the vibration pickup unit will not be significantly distorted. When the upper limit operating frequency of the vector hydrophone is 2000Hz, since a=1500μm, the detection target sound wave number k<8.4 (k=2πf/v, where v is the speed of sound in water, which is 1500m/s). The vector hydrophone designed by the present invention satisfies the condition of ka<<1 (ka<0.0125), and the sound field near the spherical vibrator will not be distorted; it can be known through theoretical analysis that the structure is reasonable.

The modal analysis of the vector hydrophone is carried out by COMSOL (Fig. 5), and the natural frequency of the vector hydrophone is 3.3KHz. Calculate the strain resistance of the hydrophone according to the varistor calculation formula ΔR=π _r σ _r +π _t σ _t , where π _r and π _t are longitudinal and transverse piezoresistive coefficients, and σ _r and σ _t are longitudinal and transverse stresses , the longitudinal piezoresistive coefficient of the P-type silicon piezoresistive strip π _r =71.8 ^-11 , the longitudinal stress in the piezoresistive region of the hydrophone is linearly distributed, and the longitudinal average stress can be used to replace σ _r , apply an acceleration load of 1g in the Z direction, and the longitudinal average stress in the piezoresistive region can be obtained Calculated ΔR＝1.4×10 ^-4 Ω; according to the output voltage of Wheatstone bridge Calculate the output sensitivity of the hydrophone, R ₀ is the resistance value of the equivalent piezoresistor R1, reference resistors R2, R3, and R4 processed by ion implantation, which is 200Ω, and U ₀ is the supply voltage of the Wheatstone bridge, which is taken as U ₀ =5V, the output sensitivity of the hydrophone is 3.5μV/g. Apply an acceleration of 1g in the horizontal direction (X or Y direction) to obtain the longitudinal average stress of the piezoresistive area on the beam And one is tensile stress and the other is compressive stress; the resistance value of equivalent piezoresistor R1 remains unchanged, so the bridge output is 0. The simulation result also shows that the present invention superimposes four common-mode signals in the vertical direction, and the differential-mode signals in the horizontal direction are mutually suppressed, which fully demonstrates that the hydrophone has common-mode output and differential-mode suppression working properties, and can be easily The sensitivity in the vertical direction can be improved, and the signal component in the horizontal direction can be suppressed; thus, the invention can well improve the resolution and sensitivity of the vector hydrophone.

Based on theory, the present invention designs and optimizes a co-vibration spherical oscillator vector hydrophone with miniaturization, good low-frequency characteristics, high sensitivity, wide operating frequency band, common-mode output and differential-mode suppression.

Description of drawings

Fig. 1 shows the structure diagram of MEMS co-vibration spherical vibrator vector hydrophone based on piezoresistive effect.

Fig. 2 shows the distribution and connection schematic diagram of the reference resistance and piezoresistor on the spherical vibrator vector hydrophone.

Figure 3 shows the schematic diagram of the Wheatstone bridge connection of the vector hydrophone.

Figure 4 shows the first-order mode diagram of the vector hydrophone.

Fig. 5 shows the stress nephogram of the structure obtained by applying 1g acceleration to the vector hydrophone in the Z direction.

Figure 6 shows the stress distribution curves on the two beams in the X direction obtained by applying a 1g acceleration to the vector hydrophone in the X direction.

In the figure: 1-frame base, 2-beam, 3-ring connector, 4-spherical vibration pickup unit, 5-metal lead, 6-welding pad.

detailed description

Specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

A MEMS co-oscillating spherical vibrator vector hydrophone based on the piezoresistive effect, including a frame-shaped base, a beam, a ring connector, a spherical polyethylene vibration pickup unit, a piezoresistor, and a reference resistor; the specific connection relationship is shown in Figure 1 , 2, the four sides on the frame-shaped base 1 are respectively connected to the annular connecting body 3 through the beam 2, and the spherical vibration pickup unit 4 is installed on the annular connecting body 3, which can be made of polyethylene material specifically. The density of vinyl pickup unit 4 is 1g/cm ³ ; piezoresistor R ₁₁ , piezoresistor R ₁₂ , piezoresistor R ₁₃ and piezoresistor R ₁₄ are set on the outside of four beams 2 respectively. The base 1 is provided with a reference resistor R2, a reference resistor R3 and a reference resistor R4; the piezoresistors R ₁₁ , R ₁₂ , R ₁₃ , and R ₁₄ are connected in series with the reference resistors R2, R3, and R4 through metal leads 5 to form Wheatstone conduction Bridge structure, as shown in Figure 3.

During the specific preparation, the vibration pickup unit such as spherical polyethylene with the same or close density as water is fixed on the ring connector; boron ions are implanted on the frame-shaped base and the outside of each beam using ion implantation technology to form a piezoresistor; The resistance value of the reference resistor on the frame base is 4 times that of the piezoresistor on the beam; the piezoresistor on the beam and the reference resistor on the frame base are connected by metal leads to form a Wheatstone bridge structure, as shown in Figure 3 Shown; Metal leads (pad connection) are used between the reference resistors and between the reference resistors and the varistor.

The frame-shaped base, the beam and the annular connector are made of SOI material through the existing MEMS process; the piezoresistor is fabricated on the outside of the beam, and the P-type silicon resistor arranged along the <110> crystal direction is made by ion implantation. Bar; make a reference resistor on a frame-shaped base, and use ion implantation to make a P-type silicon resistor bar arranged along the <110> crystal direction. Metal leads 5 and pads 8 are processed by stripping; next, ICP is used to etch the front beam and ring connector, and DRIE is used to etch the back cavity; finally, the spherical polyethylene pickup unit is bonded by the secondary integration method to the ring connector.

The outer side length of the frame-shaped base is 5000 μm, and the inner side length is 3500 μm; the beam is 900 μm long, 120 μm wide, and 30 μm thick; the outer diameter of the annular connector is 1700 μm, the inner diameter is 1500 μm, and the thickness is 30 μm; the diameter of the spherical polyethylene vibration pickup unit is 1500μm. The varistor is 100 μm long and 20 μm wide; the reference resistor is 400 μm long and 20 μm wide; the metal lead is 15 μm wide; the pad is 200 μm long and 200 μm wide.

The above are only specific embodiments of the present invention, but are not limited thereto. Any simple changes, equivalent replacements or modifications based on the present invention to solve basically the same technical problems, or achieve basically the same technical effects, all fall within the protection scope of the present invention.

Claims (5)

1. a kind of MEMS based on piezoresistive effect is with the spherical oscillator vector hydrophone of the vibration shape, it is characterised in that：Including frame-type pedestal （1）, the frame-type pedestal（1）On four edges pass through crossbeam respectively（2）Connect circular connector（3）, the circular connector （3）It is upper that spherical pick-up unit is installed（4）, the spherical pick-up unit（4）Density be 1g/cm³；Four crossbeams（2）Outside point Piezo-resistance R is not provided with₁₁, piezo-resistance R₁₂, piezo-resistance R₁₃With piezo-resistance R₁₄, the frame-type pedestal（1）On be provided with Reference resistance R2, reference resistance R3 and reference resistance R4；Piezo-resistance R₁₁、R₁₂、R₁₃ 、R₁₄With reference resistance R2, R3 after series connection Pass through metal lead wire with R4（5）Connect into wheatstone bridge configuration.

2. the MEMS according to claim 1 based on piezoresistive effect exists with the spherical oscillator vector hydrophone of the vibration shape, its feature In：Frame-type pedestal（1）Upper reference resistance resistance is crossbeam（2）4 times of upper piezo-resistance resistance.

3. the MEMS according to claim 1 or 2 based on piezoresistive effect is with the spherical oscillator vector hydrophone of the vibration shape, its feature It is：Piezo-resistance is that edge is made by the way of ion implanting<110>The P-type silicon resistor stripe of crystal orientation arrangement, it is long 100 μm, wide 20μm；Reference resistance is that edge is made by the way of ion implanting<110>The P-type silicon resistor stripe of crystal orientation arrangement, it is long 400 μm, wide 20μm。

4. the MEMS according to claim 3 based on piezoresistive effect exists with the spherical oscillator vector hydrophone of the vibration shape, its feature In：The frame-type pedestal（1）Outer 5000 μm of the length of side, 3500 μm of the interior length of side；The crossbeam（2）Long 900 μm, wide 120 μm, thick 30 μ m；The circular connector（3）1700 μm of external diameter, 1500 μm of internal diameter, 30 μm of thickness；The spherical polyethylene pick-up unit（4）Directly 1500 μm of footpath.

5. the MEMS according to claim 1 based on piezoresistive effect exists with the spherical oscillator vector hydrophone of the vibration shape, its feature In：The spherical pick-up unit（4）Prepared using polythene material.